1 Announcements & Agenda (01/22/07) You should currently be reading Ch 4! Quiz on Wednesday over Ch 3! Today: Radiation (Ch 9 – only responsible for notes) Radiation (Ch 9 – only responsible for notes) Electron energy levels (3.7) Electron energy levels (3.7) Periodic trends (3.3, 3.8) Periodic trends (3.3, 3.8)

2 Last Time: All Atoms of the Same Element Have the Same # of Protons!!! 11Na 11 protons Symbol Also, the # of protons = the # of electrons for a neutral atom

3 represents a particular isotope of an element.represents a particular isotope of an element. gives the mass number in the upper left corner and the atomic number in the lower left corner.gives the mass number in the upper left corner and the atomic number in the lower left corner. Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol: Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol: mass number 23 mass number 23 Na Na atomic number11 atomic number11 Last Time: Nuclear Symbols & Isotopes protons + neutrons

4 Listed on the periodic table Listed on the periodic table Gives the mass of “average” atom of each element compared to 12 C Gives the mass of “average” atom of each element compared to 12 C Average atom based on all the isotopes and their abundance % Average atom based on all the isotopes and their abundance % Atomic mass (!unlike mass #!) is not a whole # Atomic mass (!unlike mass #!) is not a whole # Na Last Time: The Atomic Mass is NOT the Same as the Mass Number

5 Why Do We Care About Isotopes? Answer: Nuclear Stability! “belt of stability” Unstable nuclei Radioactive Radioactive Can decay to release alpha particles, beta particles and positrons. Can decay to release alpha particles, beta particles and positrons.

6 Radiation Primer: Subatomic Particles Revisited Radiation comes from nucleus of an atom Unstable nucleus emits a particle or energy protons and/or neutrons typically lost from nucleus changing identity of element protons and/or neutrons typically lost from nucleus changing identity of element  alpha (particle)  alpha (particle)  beta (particle)  beta (particle)  gamma (pure energy)  gamma (pure energy)

7 Half-Life of a Radioisotope The time for the radiation level to fall (decay) to one-half its initial value decay curve 8 mg 4 mg2 mg 1 mg 8 mg 4 mg2 mg 1 mg initial 1 half-life 2 3

8 Examples of Half-Life Isotope Half life C sec Ra days Ra days I days C years U years

9 Medical Uses of Radiation Nuclear medicine has two main arenas Diagnostic methods Diagnostic methods Small amounts of radioisotopes administered to help image an organ or follow a physiological process Small amounts of radioisotopes administered to help image an organ or follow a physiological process Therapeutic methods Therapeutic methods Larger radiation doses to deliver fatal punch to diseased tissue Larger radiation doses to deliver fatal punch to diseased tissue

10 Diagnostic Methods Radioisotopes behave chemically the same as stable isotopes of the same atom Thus, can use to target an organ or a physiological process Usually  -emitters because radiation has to emerge from the body if the imaging equipment is to see it

11 Some Radio-Imaging Isotopes P-32Eye tumors Cr-51Spleen shape and GI disorders Fe-59Bone marrow function Se-75Pancreas scan I-131Thyroid malfunction Hg-197 Kidney scan

12 PET Scans Positron Emission Tomography Good for following physiological processes Patient given short-lived  + -emitter Patient given short-lived  + -emitter The  + hits an electron in tissues The  + hits an electron in tissues C 11 6 B 5 e+e  + t 1/2 20 min

13 PET Scans With annihilation event, a pair of gamma rays are emitted in opposite directions Very clear images because signal distinguished from background radiation (only seen in one direction) e-e- 0 2  e+e

14 A PET scan instrument places patient inside a ring of detectors to see the paired, 180 o gamma rays

15 PET Scans Can incorporate C-11 into a number of organic compounds to follow Blood flow Blood flow Glucose metabolism Glucose metabolism Oxygen uptake Oxygen uptake Find brain areas associated with epilepsy Find hard to spot tumors

16 Abnormal lymph nodes imaged by PET scan Also:

17 Therapeutic Radiation Selective destruction of pathological cells and tissues Rapidly dividing cells most vulnerable - thus it targets cancer Used when cancer is not well localized Co-60 is common source of x-rays and  -rays

18 Therapeutic Radiation Can also deliver a radiation dose with an internal administration of selected isotopes I-131 targets thyroid cancer - thyroxine contains iodine I-131 targets thyroid cancer - thyroxine contains iodine I-125 crystals implanted in prostate gland to deliver continuous radiation (t 1/2 = 60 days) I-125 crystals implanted in prostate gland to deliver continuous radiation (t 1/2 = 60 days) Y-90 implanted in pituitary to slow tumor growth everywhere Y-90 implanted in pituitary to slow tumor growth everywhere

19 Radio-Tracer Compounds Huge use of radioisotopes to study chemical reactions Can see g/L - almost individual atoms Photosynthesis - carbon in glucose comes from CO 2 Photosynthesis - carbon in glucose comes from CO 2 Calcium - uptake is 90% efficient in children; 40% efficient in adults Calcium - uptake is 90% efficient in children; 40% efficient in adults Zinc - uptake by trees in winter 2 ft/day Zinc - uptake by trees in winter 2 ft/day

20 Shifting Gears… Electron Energy Levels

21 Characteristics of Electrons Extremely small mass Extremely small mass Located outside the nucleus Located outside the nucleus Moving at extremely high speeds roughly in a sphere Moving at extremely high speeds roughly in a sphere Form the “glue” that holds compounds together Form the “glue” that holds compounds together Have specific energy levels Have specific energy levels

22 Atomic Spectra Atoms can absorb and emit radiation Absorption Usually, a source of white light passes through a sample, and the atoms absorb only specific frequencies of light. Usually, a source of white light passes through a sample, and the atoms absorb only specific frequencies of light.Emission When excited atoms emit photons, the frequencies of the photon are specific. When excited atoms emit photons, the frequencies of the photon are specific. “quantization of energy” “quantization of energy” COOL DEMO…

23 EMISSION ABSORPTION

24 A ball on a staircase shows some properties of quantized energy states.

25 Explanation for Discrete Energies: the Bohr Model First model of the electron structure of atoms Gives levels where an electron is most likely to be found Incorrect today, but a key in understanding the atom

26 Bohr Model Bohr noted the line spectra of certain elements and assumed the electrons were confined to specific energy states. These were called orbits. Line Spectra & the Bohr Model

27 Quantum Mechanics Describes the arrangement of electrons in atoms in terms of: Main or principal energy levels (n) Main or principal energy levels (n) Can describe electrons with “quantum numbers” Can describe electrons with “quantum numbers” Energy subshells Energy subshells Orbitals (space occupied within the atom) Orbitals (space occupied within the atom)

28 Electron Levels (Shells) Contain electrons that are similar in energy and distance from nucleus Contain electrons that are similar in energy and distance from nucleus Low energy electrons are closest to the nucleus Low energy electrons are closest to the nucleus Identify by numbers 1, 2, 3, 4, 5, 6….. Identify by numbers 1, 2, 3, 4, 5, 6….. The first shell (1) is lowest in energy, 2 nd level next and so on 1<2<3<4 The first shell (1) is lowest in energy, 2 nd level next and so on 1<2<3<4

29 Number of Electrons Maximum number of electrons in any electron level = 2n 2 n =12(1) 2 = 2 n =22(2) 2 = 8 n =32(3) 2 =18

30 Order of Electron Filling All electrons in the same energy level have similar (BUT NOT IDENTICAL) energy. All electrons in the same energy level have similar (BUT NOT IDENTICAL) energy. Shell 1 2 electrons Shell 2 8 electrons Shell 2 8 electrons Shell 3 18 electrons(8 first,10 later) Order of filling for the first 20 electrons Shell1234 2e8e8e2e

31 Electron Configuration Lists the shells containing electrons Lists the shells containing electrons Written in order of increasing energy Written in order of increasing energy ElementShell1 23 He2 C24C24C24C24 F2 7 Ne2 8 Al2 83 Cl28 7

32 Learning Check A. The electron configuration for sulfur 1) 2,62) 8,2,63) 2, 8, 6 B. The element in period 3 with two electrons in the outermost energy level 1) Mg2) Ca3) Be

33 Orbitals: “Locations” of the Electrons three-dimensional spaces around a nucleus where an electron is most likely to be found.three-dimensional spaces around a nucleus where an electron is most likely to be found. have shapes that represent electron density (not a path the electron follows).have shapes that represent electron density (not a path the electron follows). each orbital can hold up to 2 electrons.each orbital can hold up to 2 electrons.

34 s Orbitals An s orbital has a spherical shape around the nucleus.has a spherical shape around the nucleus. is found in each energy level.is found in each energy level. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings n = 1 n = 1 n = 2 n = 3

35 p Orbitals A p orbital has a two-lobed shape.has a two-lobed shape. is one of three p orbitals in each energy level from n = 2.is one of three p orbitals in each energy level from n = 2. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

36 Electrons in Energy Levels n = 1- 4 Energy Orbitals Maximum Total Level No. of Electrons Electrons 1 1s s 28 2p 6 2p 6 3 3s 218 3p 6 3p 6 3d10 3d10 4 4s 232 4p 6 4p 6 4d10 4d10 4f14 4f14

37 Organization of the Periodic Table s 1 s 2 p 1 p 2 p 3 p 4 p 5 p 6 s 1 s 2 p 1 p 2 p 3 p 4 p 5 p d 1 - d f 1 - f 14

38 Periodic Law All the elements in a group have the same electron configuration in their outermost shells Outermost electrons are called valence electrons Elements with same # of valence electrons display similar chemical & physical properties!!! Example: Group 2 Be2, 2 Mg 2, 8, 2 Mg 2, 8, 2 Ca 2, 2, 8, 2

39 Groups and Periods

40 Periodic Table Note: Two methods for numbering; we will use 1A, 2A, etc.

41 Metals, Nonmetals, and Metalloids The heavy zigzag line separates metals and nonmetals. Metals are located to the left.Metals are located to the left. Nonmetals are located to the right.Nonmetals are located to the right. Metalloids are located along the heavy zigzag line between the metals and nonmetals.Metalloids are located along the heavy zigzag line between the metals and nonmetals. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

42 Metals shiny and ductileshiny and ductile good conductors of heat and electricitygood conductors of heat and electricityNonmetals dull, brittle, and poor conductorsdull, brittle, and poor conductors good insulatorsgood insulatorsMetalloids better conductors than nonmetals, but not as good as metalsbetter conductors than nonmetals, but not as good as metals used as semiconductors and insulatorsused as semiconductors and insulators Metals, Nonmetals, & Metalloids

43 More Periodic Trends How Atomic Orbital filling affects: Atomic Size (Radius) Atomic Size (Radius) Ionization Energy Ionization Energy n Definitions…. Ionization Energy : Cost of removing an e - from a neutral atom Ionization Energy : Cost of removing an e - from a neutral atom Atomic Radii: Distance between center of nucleus and outer electron shell

44 Atomic Radius Within A Group Atomic radius increases going down each group of representative elements. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

45 Atomic Radius Across a Period Going across a period left to right, an increase in number of protons increases attraction for valence electrons.an increase in number of protons increases attraction for valence electrons. atomic radius decreases.atomic radius decreases. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

46 Ionization Energy In a Group Going up a group of representative elements, the distance decreases between nucleus and valence electrons.the distance decreases between nucleus and valence electrons. the ionization energy increases.the ionization energy increases. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

47 Ionization Energy Metals have lower ionization energies.Metals have lower ionization energies. Nonmetals have higher ionization energies.Nonmetals have higher ionization energies. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings